Shogun and Sterling Elite Explorer
Luton (no jokes please)
Site Reviews: 169
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One colour is for sites with reviews, the other not I believe, but I can't remember which is which. There are plenty of commercial sites which are independent of either club. It costs extra to stay on a club site as a non-member, but is entirely possible.
You could try joining the Caravan Club for a year to see how you get on, then you could also use the Certificated Locations (CLs), small sites for 5 vans which are usually less than £15 (sometimes as little as £9 or £10) per night. Some have loos and showers, some don't, most have electricity. We use these in preference to the larger club and commercial sites. The Camping and Caravanning Club has similar sites, Certified Sites (CSs). They are not Club sites as such, but affiliated to and inspected by the clubs.